Yelena G. Tropsha

Morphology and gas barrier properties of thin SiO x coatings on polycarbonate: Correlations with plasma-enhanced chemical vapor deposition conditions

Plasma-enhanced chemical vapor deposition of SiO x coatings on thermoplastics provides a viable route for production of transparent composite materials with high fracture toughness and high gas barrier properties, which are important considerations in the food packaging and biomedical device industries. By examining several series of systematically varied SiO x /polycarbonate composites, we have identified design correlations between coating characteristics (thickness, density, surface roughness, and O 2 transmission) and deposition conditions (time, power, pressure, and flow rates). Of particular interest is the observation that the thermal activation energy for O 2 permeation through these composites increases (by up to 17 kJ/mol) as their barrier efficacy increases.

Mechanisms of Oxygen and Water Diffusion Through Multilayer Inorganic/Organic Coatings

Polyethyleneterephthalate substrates were coated with thin films of silicone oxide deposited by magnetically enhanced chemical vapor deposition. The rates of oxygen and water vapor transport through the coated and uncoated film systems were obtained as a function of temperature. Activated rate theory treatment of oxygen transmission rates revealed that silicone oxide coatings were imperfect; the apparent free energies of activation (ΔEp) for transport through film substrates which were coated on a single side were statistically identical to uncoated controls. However, multilayer coatings, consisting of two silicone oxide layers separated by an organic layer resulted in a dramatic increase in the ΔEp value. Similar effects were observed in polymer films coated on both sides with identical oxide layers. A simple empirical model for the change in transport mechanism is offered to explain this unanticipated results. Activated rate theory treatment of water vapor transmission rates for these same film systems showed no obvious change in transport mechanism. However, ΔEp values obtained for water vapor permeation through silicone oxide coated polyethyleneterephthalate, polystyrene, polypropylene, and polycarbonate substrates were identical within experimental error, suggesting attractive interaction between the oxide layer(s) and water.